Question

I would like to know whether I can get source code a method on the fly, and whether I can get which file is this method in.

like

A.new.method(:a).SOURCE_CODE
A.new.method(:a).FILE

Answer 1

Use source_location:

class A
  def foo
  end
end

file, line = A.instance_method(:foo).source_location
# or
file, line = A.new.method(:foo).source_location
puts "Method foo is defined in #{file}, line #{line}"
# => "Method foo is defined in temp.rb, line 2"

Note that for builtin methods, source_location returns nil. If want to check out the C source code (have fun!), you’ll have to look for the right C file (they’re more or less organized by class) and find the rb_define_method for the method (towards the end of the file).

In Ruby 1.8 this method does not exist, but you can use this gem.